Pilots on flights between the mainland and Hong Kong will not have to calculate two different sets of measurements once an agreement with the mainland to replace the metric system with the more popular imperial method comes into effect - at least for the southern part of the Pearl River Delta.

Varying measurement units in different air zones have long caused headaches for pilots and air traffic control officers, who have to convert important data such as wind speed and altitude, increasing their workload and weighing on safety.

But in the coming decade, the southern part of the delta - including airports in Shenzhen and Zhuhai - will standardise measurements with Hong Kong's, which like most of the aviation world, plots distances in feet, the Civil Aviation Department says.

The move is aimed at smoothing management of the region's air traffic, which is expected to nearly double from 2,700 flights an hour now to 5,000 by 2020.

Civil aviation director general Norman Lo Shung-man did not say when the new arrangement would start, only that the parties had reached 'consensus'.

Standardisation of the aviation measurement system between Hong Kong and the mainland has been a touchy subject as to who should adopt whose system.

The consensus was an outcome of talks between Hong Kong, Macau and the mainland over the past three years on ways to accommodate air traffic growth and airport expansion, including Hong Kong's proposed HK$136.2 billion third runway.

Lo said the limited mainland airspace would not pose a problem for the runway project, because the Civil Aviation Administration of China had already agreed to open up the delta's airspace in stages.

Lo was speaking at the launch yesterday of the department's new air traffic control centre, which will boost the Chek Lap Kok airport's hourly capacity from 61 flights now to 68 in 2016.

By September 22, a new flight hangover point - where aircraft transfer from one air zone to another - will be added over western Macau to divert some Shenzhen-bound planes away from Hong Kong's busy airspace. This will not help boost Hong Kong's capacity but will free up more space over the airport.

3.2%

The average annual growth in Hong Kong's air traffic projected in the city's Airport Master Plan 2030